The present invention relates to a torque detecting apparatus for detecting torque applied to a rotating body and a manufacturing method of the same.
A torque detecting apparatus is described in Japanese Patent Application Laid-Open No. 2005-300267. In the torque detecting apparatus described in the Japanese Patent Application Laid-Open No. 2005-300267, a magnetic circuit forming member provided on a rotating body which has an input shaft and output shaft connected to each other via a torsion bar is enclosed by cylindrical portions disposed separately from each other in a axial direction of the input shaft, and there is provided protruding pieces projected on parts of the cylindrical portions. There are also provided two magnetism collecting rings concentrating magnetic flux which penetrates the magnetic circuit forming member, a magnetism sensitive device arranged between the protruding pieces, and a detection circuit board connected to the magnetism sensitive device.
The magnetic circuit forming member comprises a permanent magnet provided on one of the input shaft and output shaft and a magnetic ring provided on the other. It is configured to allow magnetism between the permanent magnet and the magnetic ring to vary in accordance with a rotation amount and a rotation direction thereof by relative rotation of the permanent magnet and the magnetic ring.
The magnetism collecting ring is configured to concentrate magnetic flux in the magnetic ring into the protruding piece. The magnetic sensitive device consists of a Hall element allowed to change an electric property (resistance) by action of a magnetic field. It is configured to change a detecting signal, i. e. detected torque, in accordance with a change of magnetism between the protruding pieces by the relative rotation.
The torque detecting apparatus thus configured is mounted on an electric power steering apparatus for a vehicle. The electric power steering apparatus comprises the input shaft connected to a steering wheel, a housing accommodating the input shaft to be supported, an electric motor connected to the output shaft through a decelerating mechanism, a controller consisting of a microprocessor connected to a driving circuit of the electric motor and a detector. It is configured to allow the detector to detect the rotation torque exerted to the input shaft by steering of the steering wheel based on torsion on a torsion bar, and is configured to control the electric motor to drive based on the detected torque.
FIG. 1 is a sectional view of a configuration of a torque detecting apparatus according to the prior art. The torque detecting apparatus configured as in the Japanese Patent Application Laid-Open No. 2005-300267 includes a detecting circuit board 101 connected to a magnetism sensitive device 100. After molding of the magnetism sensitive device 100 and a connecting part connecting the magnetism sensitive device 100 to the detecting circuit board 101 with a synthetic resin material, the magnetism sensitive device 100 of this molded part and the two magnetism collecting rings 102, 102 are molded with the synthetic resin material. This molding is performed as follows: disposing the two magnetism collecting rings 102, 102 in a cavity of a molding die, disposing the magnetism sensitive device 100 of the molded part between the protruding pieces 103, 103 of the two magnetism collecting rings 102, 102, and then filling the cavity with the molten synthetic resin material.